Facile Ion Diffusion and High Electrical Conductivity Enable High-Energy and High-Power Sodium-Ion Batteries from a Layered Metal-Free Cathode

Sodium-ion batteries (SIB) attract considerable attention, but their practical implementation continues to suffer in large part from the limited energy density of current SIB cathode materials. In principle, redox-active organic materials can tackle this challenge because of their high theoretical energy densities. However, electrode-level energy densities of organic electrodes are compromised due to their poor electron/ion transport and severe dissolution. Here, we report the use of a low-bandgap, conductive, and highly insoluble layered metal-free cathode material for SIBs. It has a high theoretical capacity and enables a practical-level active material content, achieving an electrode-level energy density of 606 Wh kg–1electrode and long cycle life. It allows for facile two-dimensional Na+-ion diffusion, which enables high intrinsic rate capability. In-situ growth of the active cathode material with carbon nanotubes, which improves charge transport and charge transfer kinetics, further enhances the power performance. Altogether, these allow the construction of full SIB cells built from an affordable, sustainable organic small molecule, which provide a cathode energy density of 472 Wh kg–1electrode when charging/discharging in 90 seconds, a top specific power of 31.6 kW kg–1electrode.